The fluorescent tadpoles detect how chemical compounds, such as heavy metals or endocrine-disrupting chemicals, impact the embryonic development of vertebrates. The Organization for Economic Co-operation and Development, headquartered in Paris, adopted the tadpole assay as a reference for hormonal disruptors of thyroid function. The same system screens for other toxicity effects in water systems, industrial wastes, cosmetic ingredients, and pharmaceutical manufacturing.
The fluorescent tadpoles provide more than a simple substrate/receptor detection system. Genetically engineered models are “transcriptional assays that look at downstream effects on the genetic targets of the contaminant,” says Dr. Lemkine. The tadpoles can screen for entire signaling pathways induced by a contaminant. The fluorescent response is rapid and visible within hours. Multiple markers and fluorochromes allow the detection of a number of metabolic functions and genes simultaneously.
Along with Paul Johnson, a professor of physics and astronomy at the University of Wyoming, Laramie, WatchFrog invented the Frog Box, used onsite to monitor pollutants at a water treatment facility or in a river downstream from industrial or pharmaceutical plants. The Frog Box, a two liter, double-sided chamber containing tadpoles, is placed in direct contact with the natural water source. When the tadpoles are exposed to pollutants, they fluoresce, and the amount of fluorescence is measured as they swim through a channel that connects the two sides of the Frog Box.
“We sort tadpoles on the basis of their fluorescence similar to how flow cytometers sort cells in the lab,” says Dr. Lemkine. The company has installed prototype Frog Box systems at sites in France and Spain and an experimental station may soon be set up in the U.S.
Other types of commercial toxicity models are based on worms and zebrafish, but these animals are less similar to humans. Tadpoles have metabolic and immune systems closer to humans and a more complex heart and circulatory system than zebrafish. “Amphibians are a natural model for environmental risk assessment,” says Dr. Lemkine, and “in this market we offer a novel solution.”